The present invention relates to a method for manufacturing shaped parts by polymerization of lactams in molds whereby the melt comprises at least one catalyst, at least one activator, and amino-terminated polyethers. The invention also relates to novel shaped parts manufactured according to the inventive method.
The technical manufacture of shaped parts from lactams, preferably by activated alkaline fast polymerization or block polymerization, has been in use for approximately 30 years. The term "shaped parts" in the context of the present invention refers to elements produced by known molding and polymerization techniques, including semi-finished products, shaped elements, tubes, plates, etc.
Shaped parts of lactams are produced by polymerization of lactams in casting molds and, in comparison to conventional plastic elements, for example, made of polyamide, they are, in general, harder, stiffer, and more wear-resistant. This is, in principle, due to their higher crystallinity. By determining the method-related parameters such as temperature, residence time etc. as well as by selecting the additives to be used and the post-treatment steps, the respective technological properties of the shaped parts can be influenced. Most of the aforementioned parameters, however, can only be realized with great economical and technical expenditure. The high crystallinity furthermore has the effect that the shaped parts made of lactams also have high brittleness.
Especially at low temperatures polyamides, in general, have a tendency to brittleness-related breakage, and they are also notch-sensitive. This is especially true for polyamides produced by activated anionic polymerization of lactams. This technological weakness impedes the use of shaped parts of polyamide in cold areas or in areas with great temperature fluctuations. This is especially true for rollers, gear wheels, and support elements. It is known from European Patent Application 0 167 908 to improve the impact strength of the polyamides at low temperatures by using in their manufacture amino-terminated polyethers. This resulted in good impact resistance and notch impact resistance at temperatures of 0 to 40.degree. C. by formation of polyamide block copolymers. The aforementioned European Patent Application 0 167 908 discloses a number of formulations which, however, are insufficient for the manufacture of high impact resistant shaped parts by polymerization of lactams in molds for the use in areas with temperatures below -40.degree. C. or in areas with great temperature fluctuations, also within the positive temperature range. Especially, the prior art does not provide any indication insofar as how the so-called technological properties at low temperatures can be affected, respectively, reached.
Based on this, the present invention has the object to improve a method for manufacturing shaped parts by polymerization of lactams in a mold of the aforementioned kind such that shaped parts are obtained that are useful for employment within wide temperature ranges and have, in general, good technological properties.